Also known as the Water Fiend or Destroyer, this fiend has a six-armed female human torso (about 7ft tall) atop a 15ft long snake body. They tend to wear many bangles and jewels.
Hissing fiends speak Abyssal, Celestial and Draconic, and are likely to know several mortal languages as well.
The forms of hissing fiends are based on the marilith, although any creature raised to this status is given this form.

Combat
Hissing fiends seldom rush headlong into battle, preferring to hang back and size up the situation first. They always seek to gain the best possible advantage from the local terrain, obstacles, and any vulnerability or weakness in their opponents. If they have allied creatures with them, they will tactically deploy them to cause the most trouble.
Each of the hissing fiend's six arms may wield any one-handed weapon; each individual fiend tends to prefer a particular weapon. Its tail can deliver a hard slap and may grab and constrict foes.
A popular tactic used by these fiends is to polymorph into a female human fighter to satisfy their love of battle without giving away their true nature.
Hissing fiends are proficient with all simple and martial weapons, and occasionally will learn to use an exotic weapon. They do not use armour in their natural form, but may use all armour and shields when polymorphed as a female human fighter.

Call Other (Sp): Once per round, a hissing fiend may attempt to call another fiend or entropic immortal to come to its aid. Each attempt has a 15% chance of success. There is no limit to the number of times this ability may be used, or on the total number of allies called (although no more than one ally will respond to an individual call).

Constrict (Ex): A hissing fiend deals 4d6+15 points of damage with a successful grapple check. The constricted creature must succeed on a DC 31 Fortitude save or lose consciousness for as long as it remains in the coils and for 2d4 rounds thereafter. The save DC is Strength-based. This constriction damage is in addition to the hissing fiend's normal tail damage.

Improved Grab (Ex): To use this ability, a hissing fiend must hit with its tail attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it succeeds on the grapple check, it can constrict.

Mind Power (Ex): As a swift round action, a hissing fiend may create a variety of spell-like effects at the expenditure of Power Points. A hissing fiend possesses 300 Power Points. Power Points regenerate with rest at the rate of 1 PP per minute of rest. Hissing fiends are associated with the Sphere of Entropy. The following are typical uses for the Power Points:
• A hissing fiend can cast any mortal spell at 25th level, but that costs him double the spell level in PP (for example, a fire ball would cost him 6 PP).

Spit Poison (Ex): As a standard action, a hissing fiend may spit poison at any creature within 30ft. If the fiend succeeds on a range touch attack, the victim must make a Fortitude save vs DC 31 (Con based) or suffer 3d6 Con primary and secondary damage. If the save is successful, victim still suffers 1d4 Con damage and is blinded. This blindness can only be removed by neutralise poison or cure blindness/deafness spell cast by a divine spellcaster of at least 20th level.
An immortal foe that fails the save only suffers 1d4 Con damage, primary and secondary, and is blinded for 2d10 rounds. An immortal that makes the save is unaffected.

Summon (Sp): Once per day a hissing fiend can attempt to summon 4d10 dretches, 1d4 hezrou, or one nalfeshnee with a 50% chance of success, or one glabrezu or marilith with a 20% chance of success. This ability is the equivalent of a 5th-level spell.

Control Undead (Sp): A hissing fiend may command undead as if it were a 23rd level cleric. The hissing fiend must make a turn check normally, and ignores any rebuke result. The fiend must take a standard action to give mental orders to a commanded undead. At any one time, the fiend may command any number of undead whose total Hit Dice do not exceed his effective level (23). She may voluntarily relinquish command on any commanded undead creature or creatures in order to command new ones. This ability may be used at will.

Damage Reduction (Su): A hissing fiend has damage reduction of 10/good and cold iron. Its natural attacks and any weapons wielded are treated as chaotic-aligned and evil-aligned for the purposes of bypassing damage reduction.

Enhanced Reflexes (Ex): A hissing fiend gains a +2 bonus to Initiative and its foes take a -2 penalty to all skill checks made at the beginning of an encounter to determine awareness.

Flight (Su): A hissing fiend can cease or resume flight as a free action. This ability is supernatural and it becomes ineffective in an antimagic field, and the fiend loses its ability to fly for as long as the antimagic effect persists.

Telepathy (Su): A hissing fiend can communicate telepathically with any other creature within 100 feet that has a language. It is possible to address multiple creatures at once telepathically, although maintaining a telepathic conversation with more than one creature at a time is just as difficult as simultaneously speaking and listening to multiple people at the same time.